Systems of two linear equations in two variables SAT question

Choice A is correct. The second equation in the given system defines the value of $x$ as $5y$. Substituting $5y$ for $x$ into the first equation yields $5y+y=18$ or $6y=18$. Dividing each side of this equation by $6$ yields $y=3$. Substituting $3$ for $y$ in the second equation yields $5(3)=x$ or $x=15$. Therefore, the solution $(x,y)$ to the given system of equations is $(15,3)$. 

Choice B is incorrect. Substituting $16$ for $x$ and $2$ for $y$ in the second equation yields $5(2)=16$, which is not true. Therefore, $(16,2)$ is not a solution to the given system of equations.

Choice C is incorrect. Substituting $17$ for $x$ and $1$ for $y$ in the second equation yields $5(1)=17$, which is not true. Therefore, $(17,1)$ is not a solution to the given system of equations.

Choice D is incorrect. Substituting $18$ for $x$ and $0$ for $y$ in the second equation yields $5(0)=18$, which is not true. Therefore, $(18,0)$ is not a solution to the given system of equations.